MDHS
Methods for the Determination of
Hazardous Substances
Health and Safety Laboratory
53/2
1,3-Butadiene in air
Laboratory method using
pumped samplers, thermal
desorption and gas
chromatography
August 2003
INTRODUCTION
Note: This method updates and replaces MDHS 53
(ISBN 0 11 885643 X, produced in January 1992). The
principal changes are (i) to recommend a drying pre-filter
when using Molecular Sieve 13X sorbent; (ii) to add new
validation data for Molecular Sieve 13X and for
graphitised carbon blacks as alternative sorbents.
characteristic aromatic odour. It is extremely flammable
(flash point -76°C; explosive limits approx 2-11.5% v/v
in air).
4
It is produced mainly by dehydrogenation of
n-butenes or by thermal cracking of light oil or naphtha.
Its principal use is in the manufacture of synthetic rubbers,
often in combination with styrene or acrylonitrile. It is a
starting material for many organic syntheses.
Requirements of the COSHH Regulations
Health effects
1
The Control of Substances Hazardous to Health
(COSHH) Regulations1 are designed to ensure that the
exposure of people at work to substances which could
damage their health is either prevented or, where that is
not reasonably practicable, adequately controlled.
Employers are required to make an assessment of the
health risk created by such work, and to prevent or control
exposure to the substances involved. The COSHH
Regulations also require that persons who may be
exposed to substances hazardous to health receive
suitable and sufficient information, instruction and training.
Employers must ensure that their responsibilities under
the COSHH Regulations are fulfilled before allowing
employees to undertake any procedure described in this
MDHS.
2
Guidance is given in the Approved Codes of Practice
for the Control of Substances Hazardous to Health
Regulations, the General COSHH ACOP, and the Control
of Carcinogenic Substances Regulations, the Carcinogens
ACOP, which are included in a single publication with the
COSHH Regulations.2
5
1,3-Butadiene is of low acute toxicity following single
inhalation exposure. Irritation of the eyes, nose, mouth
and respiratory tract occurs at very high concentrations.
Animal studies indicate that epoxide metabolites may be
genotoxic. 1,3-Butadiene should be regarded as a
potential human carcinogen (EU category 2).
Health and safety precautions
6
Prevention and control of exposure, emergency
procedures and health surveillance are described more
fully in HSE publications on COSHH.1-4
7
Under the Chemical Hazard and Packaging (CHIP)
Regulations,5 1,3-butadiene has been assigned the R-phrases and S-phrases:
Properties and uses
R12 Extremely flammable;
R45 May cause cancer;
S45 In case of accident or if you feel unwell seek medical
advice immediately (show the label where possible);
S53 Avoid exposure - obtain special instructions before
use.
3
1,3-Butadiene, CAS Number 106-99-0, synonym
buta-1,3-diene, CH2=CHCH=CH2, is a colourless gas of
boiling point -4°C. The liquefied gas has a vapour
pressure of 245 kPa at 21°C. 1,3-Butadiene has a
8
Following massive exposure, the patient should be
removed to a clean atmosphere, and artificial respiration
given if respiration has ceased. Contaminated clothing
should be removed. Washouts with cold running water are
1
required after splashes of the liquefied gas in the eye or
on the skin. Medical attention should be sought and, if the
patient is sent to hospital, it is recommended that the
appropriate note on treatment in the series Chemical
Exposure Treatment Cards, published by the Chemical
Industries Association, should be transmitted with the
patient (noting that exposure has been to butadiene). For
butadiene this is series 3.
Exposure limits
9
Regulation 7 of the COSHH Regulations 1999 lays
down the requirements for using maximum exposure limits
(MELs) and occupational exposure standards (OESs) for
achieving adequate control of worker exposure. The
critical health effects for the purpose of setting an
exposure limit for 1,3-butadiene are mutagenicity and
carcinogenicity. Further information is available in
Summary criteria for occupational exposure limits,
EH64/C7.6
10 For 1,3-butadiene, the Health and Safety
Commission has approved an MEL of 10 ppm (22 mg/m3),
8-hour time-weighted average. MELs are published in
EH40.7
split-ratio of a TD-GC interface. However, the magnitude
of the water problem depends on the sorbent, the type of
interface and the GC column. Some older types of thermal
desorber, coupled to a packed column with a splitless
interface, are less affected by adsorbed water. Carbon
dioxide may interfere with MS detection. The addition of a
carbon dioxide adsorption layer, eg potassium hydroxide,
is optional. Graphitised carbon black sorbents, such as
Carbopack X or Carbograph 5-TD are suitable and, based
on their performance in laboratory-based tests, the
method using Carbopack X and Carbograph 5-TD may
also comply with EN 482 and EN 1076. Carbon molecular
sieves such as Carboxen 1003, Carboxen 569 and
Carbosieve SIII are not recommended for butadiene, due
to losses that occur in storage.21
15 The method (with Molecular Sieve 13X sorbent) has
not been validated for measuring very low butadiene
concentrations typically found in ambient air. The use of
larger sampling volumes to achieve greater sensitivity may
be subject to interference by water and carbon dioxide.
Graphitised carbon black sorbents such as Carbopack X
or Carbograph 5-TD may be more suitable, based on their
performance in limited laboratory-based tests.
16 The upper limit of the useful range is determined by
the sorption capacity of sorbent, the split-ratio of the
TD-GC interface and the linear range of the GC detector.
Analytical methods
11 This is not a ‘reference’ method in the strict analytical
sense of the word. There are alternative methods
available for the determination of 1,3-butadiene.8 The use
of methods not included in the MDHS series is acceptable,
provided they have been shown to have the accuracy and
reliability appropriate to the application.
PRINCIPLE
12 A measured volume of sample air is drawn through a
metal or glass tube packed with a zeolite (Molecular Sieve
13X) or a graphitised carbon black. The butadiene gas is
sorbed and thus removed from the flowing air stream. The
collected butadiene is desorbed by heat in thermal
desorption (TD) apparatus and is transferred under inert
carrier gas into a gas chromatograph (GC) equipped with
either flame ionisation (FID) or mass spectrometer (MS)
detection.
SCOPE
13 The method described is for the determination of
time-weighted average concentrations of butadiene gas in
workplace atmospheres and can be used for the
determination of personal exposure or for fixed location
monitoring.
14 The method is suitable for sampling over periods in
the range 10 min to 8 h and concentrations in the range
0.2 to 100 mg/m3 (about 0.1 to 50 ppm) for samples of 5 l
of air. It complies with the European performance
standards EN 482:199414 and EN 1076:199715 for
workplace measurements when using Molecular Sieve
13X as sorbent, provided a drying pre-filter is fitted to
prevent adsorption of excessive water. Water vapour, if
present in sufficient quantity, may change the effective
2
17 The lower limit of the useful range depends on
detector noise, the split-ratio of the TD-GC interface and
on blank analyte levels in the sorbent tube. If the blank
level is less than 1 ng butadiene, the limit of quantification
is about 0.2 µg/m3 (0.1 ppb) for a 5 l air sample.
18 HSE Guidance Note HSG173 advises employers
about how they should conduct investigations into the
nature, extent and control of substances hazardous to
health which are present in workplace air.9 The objective
of air monitoring is usually to determine worker exposure,
and therefore the procedure described in this method is
primarily for personal sampling in the breathing zone. It
may also be used for background or fixed location
monitoring. Sampling times shorter than 30 min might be
feasible. Where the instantaneous concentration value is
fluctuating, measurement of mean concentration is valid,
provided the total sampling time exceeds the time
constant of the sampler by an adequate margin. For the
Perkin-Elmer type sampler described in this method, the
lower limit is about 15 min, although 30 min is usually the
shortest time used in validation studies. Alternative on-site
procedures, such as portable gas chromatography, infra­
red spectrophotometry or a total organic analyser, may be
used to monitor rapidly changing concentrations.
REAGENTS
Butadiene
19 This is obtainable either as pressurised pure liquefied
gas or certified mixture in a cylinder or lecture bottle.
APPARATUS
Pre-drying tube
Molecular Sieve 13X
24 Pre-drying tubes containing sodium sulphate are
commercially available. Alternatively, drying pre-filters can
be made from 25 mm 3-section filter cassettes. Use glass
fibre filters (binder-free) to retain the sodium sulphate. A
second CO2 removal layer of potassium hydroxide is
optional. It is not normally necessary to use a pre-drying
tube with Carbopack X or Carbograph 5-TD sorbents,
although it may be advisable at very high humidity in
excess of 80% RH.
20 Molecular Sieve 13X, particle size of 0.18-0.25 mm
(60-80 mesh) is one option for the sampling tubes. This
sorbent should be preconditioned by heating in an inert
atmosphere for at least 4 h at 300°C or 16 h at 250°C
before packing the tubes. Tubes prepacked to customer
specification are available commercially from some
sources. Due to the presence of up to 25% water in
untreated zeolites, the use of analytical thermal desorber
apparatus is not normally recommended for conditioning
packed tubes. Liquid water may condense in valves and
traps designed to protect valves from contamination. For
conditioning Molecular Sieve 13X packed tubes, use only
apparatus that vents water to air without intermediate
valves and traps. Examine the bulk sorbent before
packing. If there is evidence of ‘fines’ due to mechanical
damage, use an appropriate sieve to remove them.
Sampling pumps
25 Sampling pumps complying with the provisions of
BS EN 123210 with an adjustable flow rate, incorporating a
flow meter or malfunction indicator, capable of maintaining
the selected flow rate to within +5% of the nominal value
throughout the sampling period, and which people can
wear without impeding their normal work activity. The
pump should be safe for use in flammable atmospheres.
Graphitised carbon blacks
Flow meter
21 Alternatively, Carbopack X or Carbograph 5-TD is
used for the sampling tubes. These sorbents do not
normally require preconditioning before packing. The bulk
sorbent should be supplied in a granular form specified for
thermal desorption and it should not be necessary to
remove ‘fines’ before packing. Packed tubes may be
conditioned before use by heating for at least 4 h at 300°C
in a stream of inert gas. Tubes prepacked to customer
specification are available commercially from some
sources.
Sorbent tubes
22 Tubes should be compatible with the thermal
desorption apparatus to be used. Typically, but not
exclusively, they are constructed of stainless steel tubing,
6.4 mm (1/4 inch) OD, 5.0 mm ID and 89 mm long. One
end of the tube is marked, for example, by a scored ring
about 10 mm from the end. The tubes are packed with
preconditioned sorbent so that the sorbent will be within
the desorber heated zone.
23 A suggested packing procedure for 5.0 mm ID steel
tubes is to attach a small polythene funnel and preweigh
an empty tube in a small beaker. Weigh in typically 500­
800 mg Molecular Sieve 13X or 400-500 mg Carbopack X
or Carbograph 5-TD. Tap the tube gently on a hard
surface to settle the particles and press in a glass-wool
plug and retaining gauze. Gauze loading rigs capable of
applying controlled pressure to the retaining gauze are
commercially available. In the absence of a loading rig,
use light pressure and a clean metal rod about 4 mm in
diameter, for example, a sawn-off screwdriver which has
been thoroughly degreased and dried. Do not use
excessive force or the retaining gauze at the other end
may be dislodged. Check for this by tapping a freshly
packed tube on a hard surface, when no sorbent particles
should fall out.
26 Flow meter, portable, with an accuracy that is
sufficient to enable the volumetric flow rate to be
measured to within ±5%. The calibration of the flow meter
shall be checked against a primary standard, ie a flow
meter whose accuracy is traceable to national standards.
It is recommended that the flow meter used should be
capable of measuring the volumetric flow rate to within
±2% or better. Flow meters incorporated in sampling
pumps are not suitable for accurate measurement of the
flow rate. However, they can be useful for monitoring the
performance of samplers, provided they have adequate
sensitivity.
Tubing
27 Plastic or rubber tubing about 90 cm long of
appropriate diameter.
Storage end caps
28 For sealing the tubes when stored, a closed metal
end cap with PTFE ferrule (eg Swagelok™) is
recommended. End-caps made from solid PTFE with
Viton™ O-rings are acceptable for up to 3 days after
sampling (Table 2), but are not recommended for
extended storage.
Thermal desorber
29 Apparatus for the thermal desorption of the sorbent
tubes and transfer of the desorbed vapours via an inert
gas flow into a gas chromatograph will be required. A
typical apparatus contains a mechanism for holding the
tubes to be desorbed while they are heated and purged
simultaneously with inert carrier gas. The desorption
temperature and time are adjustable, as is the carrier gas
flow rate. The desorbed sample, contained in the purge
gas, is routed to the gas chromatograph via a heated
transfer line. Some types of apparatus incorporate
additional features, such as automatic sample tube
3
loading, leak-testing and a secondary cold-trap. It is
advisable to have some means of controlling the
proportion of sample reaching the gas chromatograph inlet
(split-ratio). It should be possible, within limits, to control
the split-ratio independently of the primary desorption flow.
The thermal desorber apparatus must be capable of
heating the sample tube to at least 265°C in the primary
desorption step (for Molecular Sieve 13X).
Gas-tight syringe
33 Gas-tight syringes are required for injecting butadiene
gas onto the calibration tubes. These are available
typically with PTFE-tipped plungers and push button
valves. Syringes must be in good condition and free of
PTFE flakes and particles capable of blocking the valve or
needle. This is particularly important for syringes of 100 µl
capacity or less.
Gas chromatograph
PROCEDURE
30 A gas chromatograph fitted with FID or MS detection
is suitable.
31 A wide range of chromatographic columns may be
used for this analysis. The choice will depend largely on
which compounds are present, if any, that might interfere
in the analysis. Polar packed GC columns have been used
with some older or home-made thermal desorbers.
Examples of packed columns used previously are 30%
isodecyl phthalate on Chromosorb W and 0.19% picric
acid on Carbopack C. Some examples of suitable capillary
column phases are:
●
●
●
Thick-film methylsilicone at low or sub-ambient
temperature;
Porous Layer Open Tubular (PLOT) KCl-Al2O3;
GS-GasPro PLOT (J&W/Agilent proprietary phase).
Thick-film methylsilicone capillary columns may require
sub-ambient operation for adequate resolution of
interfering C4 hydrocarbons. PLOT capillary columns do
not normally require sub-ambient operation for resolution
of C4 hydrocarbons. Retention times on KCl-Al2O3 PLOT
columns are affected by water in the samples. The
problem can be circumvented by adding a backflushable
pre-column,11 although this is difficult to manage with
conventional automated thermal desorbers. A recent study
of the effect of water on butadiene recovery used the
GS-GasPro PLOT column.12 Retention times of C4
hydrocarbons on GS-GasPro were not significantly
affected by water.
Injection unit for preparing calibration standards
32 A 1/4”
packed GC column injector may be used, either
in situ, or mounted separately. The purge gas line to the
injector should be retained. If no spare commercial injector
is available, then a septum holder could be fabricated and
attached to metal or glass tubing capable of
accommodating the 1/4”
calibration tube and a purge gas
line. One end must be threaded to take a compression
fitting with ferrule or O-ring that will secure the calibration
tube during spiking. The injection facility must allow ‘on­
column’ injection, ie the syringe needle must penetrate
inside the calibration tube to at least the depth of the fixed
gauze (if fitted), but by design the calibration tube must not
be permitted to press against the rubber septum,
otherwise the purge gas flow may be restricted. The
injection unit does not have to be heated.
4
Sorbent tubes
34 Prior to use, these should be conditioned for at least
16 h at 250°C or at least 4 h at 300°C under inert carrier
gas. When conditioning Molecular Sieve 13X, use only
apparatus venting to direct air without intermediate valves
and traps; analytical thermal desorbers are not
recommended if vented water vapour must pass through
valves and traps (paragraph 20). Tubes should then be
analysed to ensure that the thermal desorption blank is
acceptable for the intended application. If the blank is
unacceptable, the tubes should be reconditioned. Before
Molecular Sieve 13X tubes are reused for sampling, it is
recommended that a full thermal conditioning be carried
out as described. The primary thermal desorption step in
the analysis is not guaranteed to remove all water
adsorbed by Molecular Sieve 13X in sampling. It is also
advisable to check the thermal desorption blank if the
tubes are left for an extended period before use. For longterm storage of conditioned tubes, use metal end-caps
and PTFE compression fittings (ferrules), rather than
press-fit end-caps with Viton O-rings.
Collection of samples – Molecular Sieve 13X sorbent
35 Immediately before sampling, remove the end caps
from the sorbent tube and connect to the sampling pump
with appropriate tubing. The marked end of the tube
should be connected furthest from the pump and the
sample tube positioned vertically with air passing
downwards to minimise channelling. Using the shortest
connection, attach a drying pre-tube to the marked end.
When using MS detection it is recommended that carbon
dioxide adsorption on Molecular Sieve 13X is minimised
by adding a layer of potassium hydroxide in the pre-filter.
Ensure that all connections are free from leaks.
Collection of samples – Carbopack X or Carbograph
5-TD sorbent
36 Immediately before sampling, remove the end caps
from the sorbent tube and connect to the sampling pump
with appropriate tubing. The marked end of the tube
should be connected furthest from the pump and the
sample tube positioned vertically with air passing
downwards to minimise channelling. Pre-drying tubes are
not normally required, other than as a precaution when the
conditions are very humid (>80% RH).
37 When used for personal sampling, the tube should be
mounted in the worker’s breathing zone, for example on
the lapel. The pump is attached to the worker as
appropriate to minimise interference.
38 Draw a measured volume of air (about 5 l) through
the sorbent tube, remove the drying pre-tube if fitted and
replace the metal storage caps. Make sure that the PTFE
ferrules of the metal caps are fully home on the tube
before tightening. Note the unique identification number of
the tube. The sample volume is not critical, but should not
exceed the breakthrough volume of the sorbent tube. A
flow rate of 10 ml/min is recommended for 8 h sampling
and a flow rate of 200 ml/min is recommended for 10 min
sampling. If the sample is not to be analysed immediately,
store in a clean area away from source contamination. If it
is not practicable to remove the tubes from source
contamination immediately after sampling, then they
should be placed in clean uncoated sealed metal or glass
containers. Marker pens and adhesives containing
solvents should not be used to label the tubes or any
containers for storing the tubes. Do not keep sample tubes
in ambient temperatures above 30°C for more than 1-2
days. Remove to an area not exceeding 20°C and
preferably below 5°C as soon as possible, but it is not
necessary to store sample tubes in a freezer. It is
recommended to test the tightness of the metal caps after
the tubes have cooled to their storage temperature. Prior
to analysis, cooled tubes should be allowed to reach
ambient laboratory temperature before removing the metal
caps.
39 Field blanks should be prepared by using tubes
identical to those used for sampling and subjecting them
to the same handling procedure as the sample tubes,
except for the actual period of sampling. Label these as
blanks.
40 When interfering compounds are known or suspected
to be present in the air, the identity of the compounds
should be transmitted with the sample. If possible,
potential interferences for a given situation should be
checked before routine monitoring is carried out.
Breakthrough volume
41 Sampling efficiency will be 100% provided the
sampling capacity of the sorbent is not exceeded.
Breakthrough is defined as the point at which the effluent
concentration is 5% of the applied test concentration. It
may be measured by sampling from a standard
atmosphere, while monitoring the effluent air with a flame
ionisation or equivalent detector. Alternatively, a simpler
procedure is to draw air through a sorbent tube ‘spiked’
with butadiene, directly coupled to a second clean tube.
Measurement of butadiene in both tubes, as a function of
sample volume, will indicate the breakthrough volume.
This procedure, while not as rigorous as the first, is usually
adequate for the purpose.
42 The breakthrough volume as defined above varies
with ambient temperature and the concentration of
butadiene and other pollutants. It is also affected by
humidity and, to some extent, by flow rate. To allow a
suitable margin of safety, it is recommended that sample
volumes of not more than 70% of the breakthrough
volume be taken. For butadiene on Molecular Sieve 13X,
the breakthrough volume is in excess of 100 l, even in
humid air, so that breakthrough is unlikely to occur in
practice. For butadiene on Carbopack X, the breakthrough
volume has not been determined exactly, but is not less
than 25 l. For Carbograph 5-TD, the breakthrough volume
is about 10 l.
Preparation of standard ‘spiked’ calibration standards
43 Calibration standards are preferably prepared by
loading required amounts of butadiene on the sorbent
tubes from standard atmospheres using calibrated
sampling pumps, as this procedure most closely
resembles the practical sampling situation. If this is not
practicable, standards may be prepared by a gas syringe
spiking procedure, provided that the accuracy of the
spiking technique is established by using procedures
giving spiking levels traceable to primary standards of
mass and/or volume, or it is confirmed with reference
materials, if available, or with results of reference
measurement procedures.
44 In the gas syringe spiking procedure, pure butadiene
gas is obtained from a cylinder or lecture bottle by
cautiously releasing some gas into an evacuated plastic
bag fitted with a septum and flushing with gas two or three
times. Alternatively, release some gas through a length of
flexible silicone tubing (in a fume hood and away from
sources of ignition), again making sure the tubing is
adequately flushed with gas. Samples are then taken with
a gas-tight syringe, either through the septum of the bag
or wall of the silicone tubing. These samples will be used
to load sorbent tubes with known volumes of butadiene,
the mass of which can be calculated.
45 Standard ‘spiked’ calibration tubes are prepared by
injecting known amounts of butadiene gas onto clean
sorbent tubes as follows. A sorbent tube is fitted into the
injection unit (paragraph 32) through which inert purge gas
is flowing at 50-100 ml/min. Pure butadiene gas, or a
mixture of known composition, is injected through the
septum using a gas-tight syringe (paragraph 33). After
purging for 1 min, the tube is disconnected and sealed.
Prepare at least three standards at each loading level.
Prepare fresh standards with each batch of samples. The
experimental vapour density of pure butadiene gas at 0°C
and 101.3 kPa pressure is 2.476 mg/ml.13 10 µl butadiene
at 25°C is equivalent to 22.7 µg.
Analysis
46 Graphitised carbon blacks adsorb a little water if no
drying pre-tube is used in sampling. Before thermal
desorption analysis, it is advisable to remove most of the
water from Carbopack X or Carbograph 5-TD by a dry
purge of 0.5 l nitrogen or helium at ambient temperature.
The sorbent tube is then placed in a compatible TD
apparatus. In some types of TD apparatus, air is purged
from the tube to avoid chromatographic artefacts arising
from the thermal oxidation of sorbed gases and vapours.
The length of this purge step can be varied in some
models, but since the secondary cold-trap is normally
designed to be in-line at this stage, it is not as effective in
removing water from the system as dry purging off-line (it
is not possible to dry purge Molecular Sieve13X at
ambient temperature).
5
47 The tube is then heated to displace the sorbed
compounds which are passed to the GC by means of a
carrier gas stream. Generally the gas flow at this stage is
the reverse of that used during sampling, ie the backflush
direction. In the special case of butadiene on Molecular
Sieve 13X, it is recommended that the forward flush
direction be used in the primary desorption step. The
sampling recommendations (paragraph 14) and the drying
pre-filter restrict the mass of adsorbed water within
acceptable limits, but desorption in the forward flush
direction, while not essential, reduces accumulation of
water in the TD-GC system still further. Note that higher
boiling materials are not removed in this procedure and
the desorbed tubes must be conditioned in a separate
apparatus before reuse (paragraph 20).
48 The desorbed gas sample occupies a volume of
several ml and may need to be concentrated if good
chromatographic peak shape and resolution are to be
obtained. This may be achieved by using a secondary cold
trap external to the GC. Alternatively, the desorbed
sample can be passed directly to the GC where it is
concentrated by holding the column initially at a low
temperature, typically about 10°C.
49 Desorption conditions should be chosen such that
desorption from the sample tube is complete and no
sample loss occurs in the secondary cold trap, if fitted.
Typical parameters for the Perkin-Elmer ATD-400 are:
Oven
Desorb time
Desorb flow
Split ratio
Valve/transfer line
Cold trap low
Cold trap high
Cold trap sorbent
Cold trap configuration
>265°C (Mol Sieve 13X);
>150°C (Carbopack X,
Carbograph 5-TD)
10 min
20 ml/min helium
200:1
225°C
-30°C
300°C
Tenax GR (70 mg) or
Carbopack B/CMS dual-bed
backflush
ATD traps tested with ozone precursor hydrocarbons, and
equivalent to Carbopack B/carbon molecular sieve, are
commercially available pre-packed. This type of cold-trap
may be operated at up to +25°C to allow selective
elimination of water. Some experimentation with the
effects of flow rate and temperature on the recovery of
butadiene will be necessary to establish limits.
50 In the thermal desorption step, butadiene and
n-pentane (if used as internal standard) are fully recovered
from Carbopack X over the temperature range 150350°C.22 When using desorption temperatures at the lower
end of this range, less volatile hydrocarbons accumulate
on graphitised carbon blacks with repeated use, unless
the tubes are conditioned at >350°C after each
application. Butadiene is fully recovered from Carbograph
5-TD over the temperature range 150-350°C.24 n-Pentane
on Carbograph 5-TD requires a desorption temperature
>200°C.24
51 Set up the GC for the analysis of butadiene. A variety
of chromatographic columns may be used (paragraph 31).
A suitable choice might be a 60 m x 0.32 mm GS-GasPro
capillary column (J&W/Agilent). Typical operating
conditions for this column are:
6
Carrier gas
Temperature programme
Detector
helium at 140 kPa
90°C for 4 min, 4°C/min to
250°C
flame ionisation
52 The elution order of some C2-C6 hydrocarbons on
GS-GasPro under the specified operating conditions is
given in Table 1.
Table 1 Elution order of some C2-C6 hydrocarbons on
GS-GasPro, operated as specified in paragraph 51
Compound
Retention time (min)
Ethane
8.1
Propane
10.0
Isobutane
13.8
n-Butane
14.6
1-Butene
18.0
1,3-Butadiene
19.0
trans-2-Butene
19.3
Isobutylene (2-methylpropene)
19.3
cis-2-Butene
19.9
n-Pentane
21.5
1-Butyne (ethylacetylene)
n-Hexane
25.7
28.0
53 Correspondence of retention time on a single column
should not be regarded as proof of identity.
Calibration
54 Analyse each calibration standard tube by TD-GC.
Prepare a calibration graph by plotting the 10logarithm of
the areas of the butadiene peaks, corrected for blank
levels, on the vertical scale, against the 10logarithm of the
mass of butadiene loaded on the tube.
Determination of sample concentration
55 Analyse the samples and blanks as described for the
calibration standards. Determine the peak response and
read from the calibration graph the mass of the analyte in
the desorbed sample. The sorbent tube blank level for
butadiene is acceptable if it is no greater than 5 ng.
Typical levels on graphitised carbon blacks and Molecular
Sieve 13X are much less than this.
Determination of desorption efficiency
56 Ideally, the efficiency of desorption should be
checked by injecting known amounts of butadiene directly
onto the secondary trap of the TD apparatus (or directly
onto the GC column) and comparing a calibration graph
with one prepared from loaded calibration tubes. The
desorption efficiency is the response of a calibration
standard divided by the corresponding response from a
direct injection. If the desorption efficiency is less than
95%, change the desorption parameters accordingly. In
practice, the equivalence of the two methods is unlikely to
be achieved unless the TD-GC interface is splitless and
mass flow-controlled, as in some older types of apparatus
with packed columns.
57 Where the TD apparatus does not have a direct
injection facility, desorption efficiency of butadiene could
be estimated by an indirect method, using n-pentane as
an internal standard. It is assumed for the purpose of this
test that the desorption efficiency of n-pentane is 100%.
One method might be to measure the GC detector
response factor of butadiene, relative to n-pentane, by
‘spiking’ a series of butadiene/pentane mixtures on tubes
packed with an alternative carbon sorbent, such as the Air
Toxics™ dual-bed tube, then comparing relative response
factors obtained by spiking the sample tubes with the
same butadiene/pentane mixtures.
METHOD PERFORMANCE
Overall uncertainty
60 The overall uncertainty for a measuring procedure is
defined in BS EN 48214 as ‘the quantity used to
characterise as a whole the uncertainty of the result given
by a measuring procedure’, and is quoted as a percentage
combining bias and precision using the following equation
where:
Overall uncertainty =
CALCULATION OF RESULTS
x - xref + 2s
x 100
xref
where:
Mass concentration of analyte
58 Calculate the mass, in µg, of butadiene in the sample
by using the calibration graph prepared for the standard
solutions. Also calculate the mass of butadiene in the
blank samplers.
Then:
Concentration of
butadiene in air
(mg/m3)
1000 (m - mblank)
= —————————
V
where:
m
mblank
V
= mass (µg) of butadiene on sample tube;
= mass (µg) of butadiene on blank tube;
= volume of air sampled (litres).
If it is desired to express concentrations reduced to
standard conditions, eg 20°C and 101 kPa, then:
293
where:
C
P
T
= concentration (mg/m3) at actual sampling
conditions P, T;
= actual pressure of the air sampled, in kPa;
= actual temperature of the air sampled, in Kelvin.
Volume concentration of analyte
59 Alternatively, the concentration of butadiene in the
sampled air may be expressed in ppm v/v.
Cv
(ppm)
=
C
x
24.5 x T x 101
54.1
298
P
where:
Cv
=
xref
s
=
=
mean value of results of a number n of repeated
measurements;
true or accepted reference value of concentration;
the standard deviation of measurements.
An additional 5% is usually added to the overall
uncertainty percentage to allow for the variability of pump
flow rate. The performance requirements quoted in
EN 482 for overall uncertainty, where the task is
‘measurement for comparison with limit values’, are <50%
for samples in the range 0.1 to 0.5 LV and <30% for
samples in the range 0.5 to 2.0 LV (LV = limit value). From
laboratory experiments, the within-laboratory repeatability
of replicate measurements was 4-6% expressed as a
relative standard deviation. Bias with respect to the true or
accepted reference value was not determined directly, but
was estimated at up to 8% from bias due to uncorrected
desorption efficiency. Taken together with the variability of
pump flow rate, the method overall uncertainty does not
exceed ±25% in the range 0.5 to 2.0 LV.
61 The method performance standard EN 107615
recommends that, in thermal desorption, desorption
efficiency be at least 95% initially and at least 90% after
2 weeks’ storage.
Ccorr = C x 101 x T
P
x
= concentration of butadiene in air (ppm) corrected to
standard conditions;
C = concentration of butadiene in air (mg/m3) at actual
sampling conditions P, T;
24.5 = molar volume (litres) at standard conditions 293K
and 101 kPa;
54.1 = molecular weight of butadiene.
62 An accelerated Molecular Sieve 13X storage test at
40°C for 10 days12 showed significant losses of butadiene
if the tubes were purged with pure oxygen at the start of
the test. No significant losses were observed after purging
tubes with air or nitrogen and storing at 40°C for 10 days.
About 20% butadiene was lost in 7 days at 20°C when
PTFE analysis caps (Perkin-Elmer ATD-400) were used
for storage. If using the PTFE analysis caps for temporary
storage in place of metal Swagelok, no more than 3 days
should elapse between sampling and analysis.12 Another
study reported that when Molecular Sieve 13X was loaded
with 90-180 µg butadiene, recovery was as low as 60%. It
was concluded that at very high loadings, partial
polymerisation might occur on the sorbent.17 90-180 µg is
equivalent to 5-10 ppm butadiene for a 5 l sample. Similar
losses could not be confirmed at a loading of 38 µg in
another Molecular Sieve 13X study where the recovery
was about 100% after 7 days.16 Molecular Sieve 13X
storage tests in the range 1-38 µg are summarised in
Table 2. Carbopack X and Carbograph 5-TD storage tests
are summarised in Tables 3 and 4.
7
Table 2 Butadiene storage tests: % recovery from spiked Molecular Sieve 13X tubes sealed with Perkin-Elmer PTFE or
Swagelok end caps (+ s d, n = 6)
Storage time - days
Amount
µg
Temp
°C
0
3
7
14
28
PTFE
4.0
+20
100 + 4
93 + 3
77 + 10
-
-
12
Swagelok
1.3
+4
100 + 4
-
-
95 + 3
96 + 4
12
Swagelok
1.3
+20
100 + 4
-
-
96 + 10
95 + 4
12
Swagelok
6.7
+4
100 + 1
-
-
97 + 4
95 + 5
12
Swagelok
6.7
+20
100 + 1
-
-
102 + 3
97 + 2
12
Swagelok
38
+4
100 + 6
-
102 + 10
-
-
16
Storage
end cap
Refs
Table 3 Butadiene storage tests: % recovery from spiked Carbopack X tubes sealed with Swagelok caps (+ s d, n = 5)
Storage time - days
Amount
µg
µg
Temp
°C
°C
0
7
14
0.005
+20
-
95 + 3
-
21
0.4
+4
100 + 4
-
101 + 5
22
0.4
+20
100 + 4
-
96 + 3
22
8.0
+4
100 + 4
-
101 + 3
22
8.0
+20
100 + 4
-
100 + 10
22
Refs
Table 4 Butadiene storage tests: % recovery from spiked Carbograph 5-TD tubes sealed with Swagelok caps (+ s d, n = 6)
Storage time - days
Amount
µg
µg
Temp
°C
°C
0
7
14
0.4
+20
100 + 4
-
92 + 4
22
8.0
+20
100 + 2
-
99 + 5
22
Refs
63 Precision and related terms: repeatability,
reproducibility, relative standard deviation and bias are
defined in ISO 572518 or IUPAC.19
Interferences
64 Any compound that co-elutes with butadiene at the
operating conditions chosen by the analyst is a potential
interferent; changing the polarity of the GC column
stationary phase or use of a mass selective detector may
remove this interference.
65 Water is a potential interferent (paragraph 14) unless
adsorption is prevented with a drying pre-filter (for
Molecular Sieve 13X) or removed by dry purging before
analysis (for graphitised carbon blacks). Water adsorption
data for selected sorbents are summarised in Table 5.
8
QUALITY CONTROL MEASURES
66 An appropriate level of quality control should be
employed when using this method. Analytical quality
requirements, guidance on the establishment of a quality
assurance programme and details of internal quality
control and external quality assurance schemes are
described in MDHS 71.20
67 It is strongly recommended that all laboratories
undertaking the determination of hazardous substances in
workplace air should participate in an external quality
assurance scheme such as HSE’s Workplace Analysis
Scheme for Proficiency (WASP). Details of WASP are
available from the HSL website at
http://www.hsl.gov.uk/pt/pt.htm.
Table 5 Water adsorption from actively sampled air by selected sorbents packed in Perkin Elmer-type thermal
desorption tubes (refs 22, 24)
Sorbent
Temp
°C
% rel hum
Vol litres
20
42
10
66
95
20
100
6
97
93
20
47
6
0.03
0.04
4
80
6
2.3
6.2
20
100
6
9.8
9.6
20
50
10
<0.2
<0.2
20
100
6
6.8
5.6
mg water adsorbed % water adsorbed
Mol Sieve 13X
Carbopack X
Carbograph 5-TD
ACKNOWLEDGEMENTS
Molecular Sieve 13X validation data were compiled in
collaboration with Dr K J Saunders of BP, Sunbury-onThames and Dr B Fields of ICI Petrochemicals Division,
Wilton.
ADVICE
Advice on this method and the equipment used can be
obtained from the Health and Safety Executive, Health
and Safety Laboratory, Broad Lane, Sheffield, S3 7HQ,
UK (tel: 0114 2892000; fax: 0114 2892500; e-mail:
[email protected]).
The Health and Safety Executive wishes, where possible,
to improve the methods described in this series. Any
comments that might lead to improvements would
therefore be welcome and should be sent to the above
address.
APPENDIX 1 – RECOMMENDATIONS FOR THE TEST
REPORT
g) the time-weighted average concentration of
butadiene found in the air sample, in milligrams per cubic
metre or parts per million;
h)
the overall uncertainty of the method;
i)
the mean temperature and pressure during the
sampling period, if appropriate (paragraphs 58 and 59);
j)
the name of the person who collected the sample;
k)
the name of the analyst;
l)
the date of the analysis;
m)
any unusual features noted during the determination.
If necessary data (eg the volume sampled) are not
available to the laboratory for the above calculations to be
carried out, the test report may contain the result in
micrograms of butadiene per sample.
APPENDIX 2 – DESCRIPTION OF SORBENT TYPES
It is recommended that the test report should include the
following information:
a) a complete identification of the sample, including the
date and place of sampling;
b) reference to this MDHS and a description of any
deviation from the procedures described;
c)
the type and size of sample tube used;
d)
the type of pre-filter used, if appropriate;
e) the make and type of sampling pump and flow meter
used, the primary standard against which it was
calibrated, and the range of flow rates for which the flow
meter was calibrated;
Molecular Sieve 13X
Carbopack X
Carbograph 5-TD
Carbopack B
Carbotrap
Air Toxics dual-bed
Carboxen 1003
Carboxen 569
Carbosieve SIII
sodium aluminosilicate zeolite
graphitised carbon black
graphitised carbon black
graphitised carbon black
graphitised carbon black
graphitised carbon black +
carbon molecular sieve
carbon molecular sieve
carbon molecular sieve
carbon molecular sieve
Carbopack™, Carbosieve™, Carbotrap™ and
Carboxen™ are trade marks of Sigma-Aldrich (Supelco).
Carbograph™ is a trade mark of Alltech Associates.
f)
the duration of the sampling time in minutes and/or
the time at the start and the end of the sampling period;
9
REFERENCES
1
COSHH essentials: Easy steps to control chemicals.
Control of Substances Hazardous to Health Regulations
HSG193 HSE Books 1999 ISBN 0 7176 2421 8
2
Control of substances hazardous to health. The
Control of Substances Hazardous to Health Regulations
2002. Approved Code of Practice and guidance L5
(Fourth edition) HSE Books 2002 ISBN 0 7176 2534 6
3
COSHH: A brief guide to the regulations: What you
need to know about the Control of Substances Hazardous
to Health Regulations 2002 (COSHH) Leaflet
INDG136(rev2) HSE Books 2003 (single copy free or
priced packs of 10 ISBN 0 7176 2677 6)
4
The technical basis for COSHH essentials: Easy steps
to control chemicals HSE Books 1999 ISBN 0 7176 2434 X
5
Approved supply list. Information approved for the
classification and labelling of substances and preparations
dangerous for supply. Chemicals (Hazard Information and
Packaging for Supply) Regulations 2002. Approved list L129
(Seventh edition) HSE Books 2002 ISBN 0 7176 2368 8
6
Summary criteria for occupational exposure limits
Environmental Hygiene Guidance Note (Loose leaf
binder) EH64 HSE Books 2002 ISBN 0 7176 2569 9
7
Occupational exposure limits: Containing the list of
maximum exposure limits and occupational exposure
standards for use with the Control of Substances Hazardous
to Health Regulations 1999 Environmental Hygiene
Guidance Note EH40 (revised annually) HSE Books 2002
ISBN 0 7176 2083 2
8
Bianchi A, Boyle B, Harrison P, Lawrie P, Le Lendu T,
Rocchi P, Taalman R and Wieder W A review of analytical
methods and their significance to subsequent occupational
exposure data evaluation for 1,3-butadiene European
Chemical Industry Council (CEFIC) Report D/1997/3158/3
February 1997
9
Monitoring strategies for toxic substances HSG173
HSE Books 1997 ISBN 0 7176 1411 5
10 British Standards Institution Workplace atmospheres
- Pumps for personal sampling of chemical agents ­
Requirements and test methods BS EN 1232:1997
11 Lunsford RA and Gagnon YT Use of a backflushable
pre-column to maintain the performance of an Al2O3 PLOT
fused silica column for the determination of 1,3-butadiene
in air High Resolut Chromatogr 10 1987 102
12 Wright MD and Plant NT 1,3-Butadiene monitoring:
Thermal desorption pumped/diffusive methods Health and
Safety Laboratory report 2001 OMS/2001/15
13 Nelson G Gas mixtures: Preparation and control
CRC Press LLC 1992 Appendix E
10
14 British Standards Institution Workplace atmospheres
- General requirements for the performance of procedures
for the measurement of chemical agents European
Standard BS EN 482:1994 ISBN 0 580 236447
15 British Standards Institution Workplace atmospheres ­
Pumped sorbent tubes for the determination of gases and
vapours - Requirements and test methods BS EN 1076:1997
16 Cox PC Back-up data report: Pumped sorbent tube
method for butadiene Health and Safety Executive report
IR/L/AO/85/11 1985
17 Tindle P and Loader E Shell Research Thornton
2000 unpublished data
18 ISO Standard 5725-1:1994 Accuracy (trueness and
precision) of measurement methods and results – Part 1:
General principles and definitions
19 IUPAC Harmonised protocols for the adoption of
standardised analytical methods and for the presentation of
their performance characteristics Pure and Appl Chem 62
1990 149-162
20 Analytical quality in workplace air monitoring
MDHS71 HSE Books 1991 ISBN 0 7176 1263 5
21 Dettmer K, Knobloch Th and Engewald W Stability of
reactive low boiling hydrocarbons on carbon based
adsorbents typically used for adsorptive enrichment and
thermal desorption Fresenius J Anal Chem 366 2000 70-78
22 Gostlow K, Plant NT and Wright MD Evaluation of
carbon sorbents for the determination of 1,3-butadiene in
air by thermal desorption Health and Safety Laboratory
Report 2002 OMS/2002/13
23 Sunesson A-L, Sundgren M and Levin J-O 1,3Butadiene in air – Evaluation of Carbopack X for diffusive
sampling and thermal desorption-gas chromatographic
analysis Proceedings of Airmon 2002 4th International
Symposium on Modern Principles of Air Monitoring
3-7 February 2002 Lillehammer Norway
24 Plant N, Cann A and Wright MD 1,3-butadiene
monitoring – Validation of Carbograph 5-TD Health and
Safety Laboratory Report 2001 OMS/2001/25
11
TITLES IN THE MDHS SERIES
1
2
3
4
5
6/3
10/2
12/2
14
15
16
17
18
19
20
21
22
23
24
25/2
26
27
28
29/2
30/2
31
32
33
35/2
36
37
38
39/4
40
41/2
42/2
43
44
45
46/2
47
48
49
50
51/2
52/3
53/2
Acrylonitrile charcoal tube/gas chromatography (GC)
Acrylonitrile pumped thermal desorption/GC
Standard atmospheres syringe injection
Standard atmospheres permeation tube
On-site validation of methods
Lead atomic absorption (AA)
Cadmium AA
Chromium AA
Total inhalable and respirable dust gravimetric
Carbon disulphide charcoal tube/GC
Mercury adsorbent tube (Hydrar) AA
Benzene charcoal tube/GC
Tetra alkyl lead continuous monitoring
Formaldehyde colorimetric (Chromotropic acid)
Styrene pumped charcoal tube/GC
Glycol ethers charcoal tube/GC
Benzene thermal desorption/GC
Glycol ethers thermal desorption/GC
Vinyl chloride charcoal tube/GC
Organic isocyanates reagent bubbler/HPLC
Ethylene oxide charcoal tube/GC
Diffusive sampler evaluation protocol
Chlorinated hydrocarbons charcoal tube/GC
Beryllium AA
Cobalt AA
Styrene pumped thermal desorption/GC
Phthalate esters solvent desorption/GC
Adsorbent tube standards
HF and fluorides ion-selective electrode
Toluene charcoal tube/GC
Quartz in respirable airborne dust direct infra-red
Quartz in respirable airborne dust KBr disc technique
Asbestos fibres light microscopy (European reference
version)
Toluene thermal desorption/GC
Arsenic AA
Nickel AA
Styrene diffusive/thermal desorption/GC
Styrene diffusive/solvent desorption/GC
Ethylene dibromide solvent desorption/GC
Platinum AA
Rubber fume in air measured as total particulates
and cyclohexane soluble material
Newspaper print rooms: measurements of total
particulates and cyclohexane soluble material in air
Aromatic isocyanates acid hydrolysis/ diazotisation
Benzene diffusive/thermal desorption/GC
Quartz in respirable dusts X-ray diffraction (direct method)
Hexavalent chromium in chromium plating mists
colorimetric (1,5-diphenylcarbazide)
1,3 Butadiene thermal desorption/GC
54
Protocol for assessing the performance of a pumped
sampler for gases and vapours
55
Acrylonitrile diffusive/thermal desorption/GC
56/2 Hydrogen cyanide ion-selective electrode
57
Acrylamide liquid chromatography
59
Manmade mineral fibres
60
Mixed hydrocarbons
61
Total hexavalent chromium compounds in air colorimetric
62
Aromatic carboxylic acid anhydrides
63
Butadiene diffusive/thermal desorption/GC
64
Toluene charcoal diffusive/solvent desorption/GC
65
Mine road dust: determination of incombustible matter
66
Mixed hydrocarbons (C5 to C10) in air diffusive/
thermal desorption/GC
67
Total (and speciated) chromium in chromium plating mists
colorimetric (1,5-diphenylcarbazide)
68
Coal tar pitch volatiles
69
Toluene diffusive/solvent desorption/GC
70
General methods for sampling airborne gases and vapours
71
Analytical quality in workplace air monitoring
72
Volatile organic compounds in air
73
Measurement of air change in factories and offices
74
n-Hexane in air diffusive/solvent desorption/GC
75
Aromatic amines solid sorbent/thermal desorption/GC
76
Cristobalite in respirable dusts X-ray diffraction
(direct method)
77
Asbestos in bulk materials
78
Formaldehyde diffusive/solvent desorption/liquid
chromatography
79
Peroxodisulphate salts mobile phase ion chromatography
80
Volatile organic compounds diffusive/thermal desorption/GC
81
Dustiness of powders and materials
82
The dust lamp
83
Resin acids GC
84
Oil mist from mineral oil-based metalworking fluids
85
Triglycidyl isocyanurate in air pumped filter/
desorption/liquid chromatography
86
Hydrazine in air
87
Fibres in air
88
Volatile organic compounds in air diffusive/solvent
desorption/GC
89
Dimethyl sulphate and diethyl sulphate thermal
desorption/GC-mass spectrometry
90
Alkyl 2-cyanoacrylates liquid chromatography
91
Metals and metalloids XRF
92
Azodicarbonamide high performance liquid
chromatography
93
Glutaraldehyde HPLC
94
Pesticides pumped filters/sorbent tubes/GC
95/2 Metalworking fluid AA/plasma-atomic emission
spectrometry
96
Volatile organic compounds in air pumped solid
sorbent/solvent desorption/GC
100 Asbestos-containing materials
© Crown copyright 2003
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